I am not sure if others use Virtual Box, but the most recent versions seem to have bugs that may affect VMs used to run KVS. More specifically, I found that 5.1.8 and 5.0.28 both cause problems with Windows XP SP3 (e.g., network timeouts); for other versions of Windows, YMMV.

If this happens to you, you might want to downgrade back to 5.0.26, which seems to work fine for XP SP3 (and possibly others).